small improvements
temporarily fixed a splicing bug in set patterns. needs revisiting
later.
bug hunting
fixed very subtle bug in extend (flags needed to be extended before
anything else in order to allow overloading of constructors)
fixed nasty lex/cf issue
fixed parsing concrete fragments in the shell
fixed some typos in the parser generator
working to make all tests succeed (by adapting tests to new
circumstances)
fixed minor issues
solved a possible infinite recursion